1. Field of the Invention
The present invention relates to an abnormality detecting method and device for a position detecting device which is applicable for both a rotational position and a linear position such as a rotational position detector, for example a resolver or a synchro for detecting a position, or a linear position detector based on the similar detection principle, and an electric power steering device using such a device, and particularly, relates to judgment at the time of abnormality in the position detection of an electric power steering device for assisting a steering effort of a steering wheel by means for a motor, and a processing at that time.
2. Description of the Prior Art
Conventionally, in this kind of position detecting device, a resolver is used as a position detecting sensor, and two orthogonal winding output signals are inputted into a resolver digital converter (R/D converter), and the rotational position is detected. This position detecting device is utilized in the control of rotation of a motor.
FIG. 5 is a block diagram showing a position detecting device disclosed in, for example, Japanese Patent Laid-Open No. 9-72758.
In this drawing, a reference signal that is sine wave voltage for excitation is inputted into the position sensor 1 using a resolver from an oscillator circuit 22. From the position sensor 1, a reference signal is outputted as a signal amplitude-modulated by cos xcex8 and sin xcex8 according to the rotational position xcex8 thereof. Hereafter, an output signal amplitude-modulated by cos xcex8 is a cos signal and an output signal amplitude-modulated by sin xcex8 is a sin signal.
These two output signals are inputted into a position detector circuit 4 using an R/D converter, and from the position detector circuit 4, the rotational position xcex8 is outputted as a digital signal. This digital signal of the rotational position xcex8 is inputted into a control CPU 5, and is used for a predetermined control. In the case where a breaking of the wire is caused in the resolver used as the position sensor 1, it becomes a cause of malfunction in various control mechanisms, and therefore, it is necessary to detect this breaking of the wire of the resolver without delay.
As this kind of conventionally used abnormality detecting method, in the above described Japanese Patent Laid-Open No. 9-72758 or the like, there is disclosed a method in which the amplitude-modulated signals (sin signal, cos signal) of two output parts of the position sensor 1 corresponding to the rotational position that are resolver signals are compared or operated in the control CPU 5 through the A/D converter circuits 23, 24 apart from the position detector circuit 4 for detecting the position, and abnormality is judged in the case where a predetermined condition is not satisfied.
Furthermore, in Japanese Patent Laid-Open No. 2000-131096 shown in FIG. 6, a DC power source 12 is connected to one end of an output winding 3 of the position sensor 1 through a resistance 31, and the other end of the output winding 3 is connected to the ground through a resistance 32, and consequently, DC bias current 15 is applied to the cos signal or sin signal that is amplitude-modulated according to the rotational position, from the output winding 3 of the position sensor 1. Then, signals 6, 7 from the output winding 3 are inputted in a differential amplifier 10 through buffer circuits 8, 9, respectively and are amplified, and abnormality is judged when a signal with a voltage value higher than the maximum voltage value is outputted from the amplified signal.
Object of the Invention
By the way, the conventional abnormality detecting methods disclosed in the above described specification have the following problems.
First, in the above described Japanese Patent Laid-Open No. 9-72758, the structure is made as mentioned above, and therefore, for example, as for the sin signal, it becomes of 0 V when the rotational position is of 0 degree since it is an amplitude-modulated signal, and the judgment cannot be made when the wiring is broken. Furthermore, it is impossible to detect a grounding or air discharge, and it is impossible to judge that it is abnormality.
Furthermore, in the case of the above described Japanese Patent Laid-Open No. 2000-131096, the normal time and abnormal time are judged by detecting the maximum value voltage of the amplified signal from the amplitude-modified signal, and therefore, a circuit for dividing the normal time and the abnormal time by a wind comparator or the like is necessary. Furthermore, it is necessary to input the signal from the output winding 3 of the position sensor 1 to the differential amplifier 10 through the buffer circuits 8, 9. Therefore, there is a tendency of enlarging the circuit scale for detecting the breaking of the wire, which is expensive.
Furthermore, noise is easily generated since the passage of the output winding 3 is usually long, and a resistance 33 is usually arranged between the output parts as shown in FIG. 7, and it is the ordinary course that the high frequency component noise is eliminated by controlling the impedance. However, in the case of the circuit structure of FIG. 6, it is difficult to detect the breaking of the wire because of the bias resistance, that is, the resistances 31, 32 when the above described resistance 33 is arranged between the output parts, and accordingly, the resistance 33 cannot be arranged, and therefore, it is impossible to eliminate the noise.
This invention is made for solving such problems, and it is an object to provide an abnormality detecting method and a device of a position detecting device in which DC bias is applied to the output winding of the position sensor, and the abnormality such as the breaking of the output winding is surely detected, and in the meantime, the DC bias and the reduction of noise in the position detecting can coexist, and the cost is low and the structure is simple, and an electric power steering device.
The abnormality detecting method of a position detecting device according to the invention of claim 1 is an abnormality detecting method of a position detecting device which generates an amplitude-modulated or phase-modulated signal from a position sensor according to a rotational position of a rotor when a reference signal having a predetermined periodic waveform is supplied, and the method comprises: a step of applying DC bias current to an output winding of the above described position sensor; a step of detecting a biased DC signal of an amplitude-modulated or phase-modulated signal applied to the above described output winding, apart from signal processing for detecting a rotational position of the above described rotor; and a step of judging abnormality of the above described position detecting device from the above described detected DC signal.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected regardless of the rotational position of a rotor, and furthermore, simplification of the circuit structure and reduction of the cost can be attained.
The abnormality detecting method of a position detecting device according to the invention of claim 2 is a method, in which the above described step of detecting the DC signal includes a step of eliminating an amplitude-modulated component or a phase-modulated component produced by noise and a reference signal.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected without being affected by noise coming from the outside or the like.
The abnormality detecting method of a position detecting device according to the invention of claim 3 is a method further comprising a step of judging abnormality of the above described position detecting device from a DC signal depending on only the above described DC bias current, when the above described reference signal is not supplied.
According to this configuration, there is such an effect that the accuracy in abnormality detection of the position detecting device can be improved.
The abnormality detecting method of a position detecting device according to the invention of claim 4 is a method, in which it is judged that the above described position detecting device is abnormal when the state where the above described DC signal is out of a predetermined range continues for a predetermined time, in the above described step of judging abnormality.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected without being affected by noise from the outside or the like.
The abnormality detecting device of a position detecting device according to the invention of claim 5 is an abnormality detecting device of a position detecting device which generates an amplitude-modulated or phase-modulated signal from a position sensor according to a rotational position of a rotor when a reference signal having a predetermined periodic waveform is supplied, and the abnormality detecting device comprises: bias current applying means for applying DC bias current to output winding of the above described position sensor; DC signal detecting means for detecting a biased DC signal of an amplitude-modulated or phase-modulated signal applied to the above described output winding, apart from signal processing means for detecting a rotational position of the above described rotor; and abnormality judging means for judging abnormality of the above described position detecting device from a DC signal detected by the above described DC signal detecting means.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected regardless of the rotational position of the rotor, and furthermore, simplification of the circuit structure and reduction of the cost can be attained.
The abnormality detecting device of a position detecting device according to the invention of claim 6 is a device, in which the above described DC signal detecting means has a filter of eliminating an amplitude-modulated component or a phase-modulated component produced by noise and a reference signal.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected without being affected by noise from the outside or the like.
The abnormality detecting device of a position detecting device according to the invention of claim 7 is a device, in which the above described filter has a time constant larger than an oscillation period of the above described amplitude-modulated or phase-modulated signal.
According to this configuration, there is such an effect that it is possible to contribute the improvement of accuracy in the abnormality detection of the position detecting device.
The abnormality detecting device of a position detecting device according to the invention of claim 8 is a device, in which the above described filter includes a resistance and a capacitor that are connected in series between both ends of the above described output winding and the ground, respectively.
According to this configuration, there is such an effect that noise appearing on the output winding can easily be eliminated, and it is possible to contribute the improvement of accuracy in abnormality detection of the position detecting device.
The abnormality detecting device of a position detecting device according to the invention of claim 9 is a device, in which the above described filter uses either the resistance or the capacitor that is connected in series between both ends of said output winding and the ground for the abnormality detection.
According to this configuration, there is such an effect that it is possible to contribute the improvement of accuracy in abnormality detection of the position detecting device.
The abnormality detecting device of a position detecting device according to the invention of claim 10 is a device, in which the above described bias current applying means includes a passage that leads to the ground from a DC power source through a first resistance, one resistance of the above described filter, the above described output winding, the other resistance of the above described filter, and a second resistance.
According to this configuration, there is such an effect that it is possible to contribute the improvement of accuracy in the abnormality detection of the position detecting device, the simplification of the circuit structure, and the reduction of the cost.
The abnormality detecting device of a position detecting device according to the invention of claim 11 is a device, in which the amount of resistance included in the passage of the above described bias current applying means is set larger than the amount of resistance applied between the above described output winding.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected without giving adverse effects on the amplitude-modulated or phase-modulated signal.
The abnormality detecting device of a position detecting device according to the invention of claim 12 is a device further comprising reference signal generating means capable of controlling generation of a reference signal, in which the above described abnormality judging means judges abnormality of the above described position detecting device from a DC signal depending on only the above described DC bias current, when the above described reference signal is not supplied.
According to this configuration, there is such an effect that accuracy in the abnormality detection of the position detecting device can be improved.
The electric power steering device according to the invention of claim 13 comprises: the abnormality detecting device of a position detecting device according to any one of the above described claims 5 to 11; control means for controlling a controlled object including the above described rotor on the basis of a position signal outputted from the above described position detecting device; and monitoring means for monitoring the control operation of said control means, and it inputs an abnormality detecting signal based on a DC signal obtained by the above described abnormality detecting device directly to the above described control means or the above described monitoring means, and it judges that the above described position detecting device is abnormal when the above described abnormality detecting signal is out of a predetermined range.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected regardless of the rotational position of the rotor, and furthermore, simplification of the circuit structure and reduction of the cost can be attained.
The electric power steering device according to the invention of claim 14 is a device, in which it is judged that the above described position detecting device is abnormal when the state where the above described DC signal is out of a predetermined range continues for a predetermined time.
According to this configuration, there is such an effect that abnormality of the position detecting device can surely be detected without being affected by noise from the outside or the like.
The electric power steering device according to the invention of claim 15 is a device, in which the above described controlled object is a motor of assisting the steering effort of a driver, and driving means for driving the above described motor is provided, and when it is judged from the above described abnormality detecting device that the position detecting device is abnormal, driving control of the above described motor is stopped, and driving of the above described motor is inhibited.
According to this configuration, there is such an effect that malfunction in the motor driving control can surely be stopped.